Solution-processed hybrid organolead trihalide (MAPbX3) perovskite solar cells (PSCs) have now achieved 20.1% certified power conversion efficiencies (PCE), following a rapid surge of development since perovskite-based devices were reported in 2009. A key to the success of PSCs is the long diffusion length of charge carriers in the absorber perovskite layer. This parameter is expected to depend strongly on film crystallinity and morphology, so it is expected that there may be room to improve upon already remarkable PSC efficiencies via the optimization of three key parameters: charge carrier lifetime, mobility, and diffusion length.